My car is overheating. I check the oil for coolant or water to see if it's the head gasket. I believe it's the thermostat. my question is what's the difference between the $10 & $30? how difficult is to install, what is the procedure and what tools are required?

The most common reason for oil and water mixing is a blown head gasket. This can also cause a low coolant level that can affect the heaters on the vehicle. It could also be worth checking the coolant thermostat as that is also a common reason for overheating.

I DON'T KNOW. YOU MAY WANT TO CHECK YOUR THERMOSTAT. IF REMAINING CLOSED, ENGINE MAY BOIL ANTIFREEZE AND VAPORIZE OILS.

Most likely a blown head gasket or cracked head, maybe both.

overheating sound like faulty thermostat.thermostat either sticking close or could have blown headgasket if you see a lot of white smoke coming out of exhaust.if headgasket is leaking check engine oil should look milky.also check water pump look around weep hole or see coolant leaking around water pump replace water pump.also check water pump drive belt.make sure drive belt not loose slipping.

you my have thick smoke coming out of your tail pipe or oil leaking out on to your engine

Oil and coolant mixed usually means the engine is damaged.
Blown head gasket, or cracked block - head.
You may have coolant in the engine oil too.
I would not drive it.

OVERHEATING CAN BE CAUSE BY MANY THINGS LIKE FAULTY THERMOSTAT AND FAULTY RADIATOR PRESSURE CAP,TOO MUCH WATER IN COOLANT SYSTEM NEED 50 / 50 WATER AND ANTIFREEZE.LOOK FOR WATER PUMP WEEP HOLE LEAK, IF COOLANT LEAKING OUT WEEP HOLE WATER PUMP BAD NEED REPLACING.CHECK FOR LOW COOLANT LEVEL, YOUR RADIATOR OVERFLOW JUG SHOULD HAVE COOLANT AT THE FULL COLD MARK IF NOT KEEP ADDING COOLANT INTO COOLANT OVERFLOW JUG UNTIL COOLANT STOP DROPPING AND FULL COLD MARK, IF OVERFLOW COOLANT JUG WAS EMPTY RADIATOR IS LOW ON COOLANT.WHICH CAUSE AIR IN COOLANT SYSTEM KEEPING THE ENGINE COOLANT TEMPERATURE SENSOR FROM BEING SUBMERGE IN HOT COOLANT WHICH TURN ON THE COOLANT FANS.WHEN ENGINE COOLANT TEMPERATURE GET CERTAIN SET TEMPERATURE LIKE 190 DEGREES THE PCM AND COOLANT SENSOR WILL TURN ON COOLANT FANS, IF VECHICLE OVERHEATING COOLANT FANS NOT WORKING EITHER YOU HAVE FAULTY ENGINE COOLANT TEMPERATURE SENSOR CHECK COOLANT FANS FUSE AND RELAYS. YOU CAN CODE SCAN CAR TO SEE IF YOU HAVE FAULTY PCM, FAULTY ENGINE COOLANT TEMPERATURE SENSOR OR FAULTY COOLANT FAN RELAY.IF COOLANT FAN AND ENGINE COOLANT TEMPERATURE SENSOR OKAY,YOU HAVE CORRECT COOLANT LEVEL IN COOLANT SYSTEM, THERMOSTAT AND RADIATOR PRESSURE CAP BEEN REPLACED, YOU COULD HAVE BLOWN HEAD GASKET CHECK ENGINE OIL LOOKS LIKE MILK SHAKE HEAD GASKET BLOWED ALSO WHEN HEAD GASKET BLOWED YOU CAN DRIVE CAR SHORT DISTANCE START OVERHEATING AND YOU LOOSE ENGINE POWER SUSPECT BLOWED HEAD GASKET.

Need to seal the leak in the coolant container with epoxy or by replacing the coolant container.

Fill coolant system with 50/50 solution up to 2 gallons may be required to stop the overheating.

Don't drive an overheated engine.

I don't see where you replace thermostat, when replacing water pump very good idea to also replace thermostat, if you done that and stillls over heat's, then you will need to do a block test any repair shop can do this or you can buy a test block kit at any auto part's, this test will let you know if you have bad cylinder head gasket's, you will not always get water in the oil when head gasket's are bad, about the only time that you get oil in coolant is if you have bad in take gasket, check oil dip stick for water.

Might be blown head gasket. Is there oil in the coolant or coolant in the oil? Either of these would tell you that.
Also the exhust can get into the coolant and make the coolant low all the time.
I had two Chrysler products that the exhaust forced coolant out and had a bad head gasket.